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Home Forums General Discussion Geothermal energy

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    As far as I understand, there are basically two kinds of useful geothermal energy, one is available in areas such as Iceland where the heat from the earth’s core is available close to the surface, or at least within boring distance. These rocks are hot enough to turn water to steam and can be used to generate electricity in much the same way as a conventional power station. This heat can also heat homes factories etc.

    The other kind is made use of in ground source heat pumps. These basically work in the same way as a refrigerator, only the layout is different. Heat from the sun is absorbed by the soil and rocks and leaks out relatively slowly overnight. If you go say a metre down the soil doesn’t freeze even in winter, at least in the uk. This is the heat you are making use of. Laying pipes at this depth corresponds to the inside of your fridge, which is connected to radiators, usually underfloor inside your house, which corresponds to the back of your fridge where all the black pipes are. In your fridge these pipes get warm as they remove the heat from the food you want to keep cold.

    Energy is used to compress the gas inside your system before returning it underground, but in return you get three times the energy (rough figures) heat as you put in as electricity, so it can be a cheap way to heat a house if you are prepared to dig up your garden. This electricity could even come from solar panels, PV type, to make the whole system independent of the grid. Car parks are good places to bury pipes because the tarmac or whatever is dark and so absorbs heat well.

    Finally it is being used in the UK.


    Can any one tell me the requirements for this and can anyone access it? Is it being used in the UK? I understand it is becoming very popular in France.


    Hi there !

    Wikipedia has some good information and great photographs to explain the system.

    Here’s more information on “puis Canadiens” or heat pumps – good for DIY projects :

    If you type “puis Canadien” in your browser, you’ll find a lot of information on the ‘net, but the best sites and blogs are in French.


    Ground source heat pumps will cost a lot to install. like – A LOT. its not normally the best solutions. The ground is at a constant temp. of about 11 degrees so they basically just tap this. if you’re fortunate to stumble on a hot spring then by all means tap away!


    If you want more info my company specify them for various eco-buildings, we don’t do that many as we do a mix of renewables but i need ot learn a lot more about it so im happy to delve in further.

    Nick Rosen

    As a part of the Renewable Energy Industry I wanted to share some insight into the cost benefits of Geothermal Heating and Cooling. This IS the most efficient way of

    generating energy based on the COP (coefficiency of performance) which simply means what you get vs. what you paid for. Sourcing your energy close to the load (house,building) with the earths constant temp of 55-62F underneath the surface means you have to pay only for the amount of energy extraction needed to reach comfortable levels in a given structure. Usually 70 degrees cooling and 72-73 heating. That means paying for 7-10 degrees of heating or cooling as opposed to starting from zero to reach 70-73 degrees. That is where the cost savings are.

    Sure , capital costs are steeper initially but if you consider your investment

    over the long term with the net present value of energy today and an aging infrastrucure you can see the value. Let me know your thoughts …


    Here’s the thing folks (just my two cents)…

    Geothermal is great…but…not for off-gridding…the premise being, those compressors are electricity hogs…unless you stack two inverters, you can’t supply the 220 volt power needed for the compressors, notwithstanding the 30+ amps needed to run them. They simply have too much draw. This is the same reason why air conditioners are too expensive to run on an off-grid system…220 volt at 30 amps is waaayyyyy too much power draw….stick with simplicity…solar hot water with a couple of small grundfos pumps, energy efficient heat exchanger…that is doable…220v and 30 amps, though doable, is too expensive for many people to supply…


    There is a surprising amount of energy in the ground around your home that can be harnessed in order to heat your house effectively and inexpensively.

    The use of geothermal heat pumps can be a fantastic way to alleviate your energy costs and provide heat for your home using renewable and environmentally friendly sources.

    Geothermal heat pumps harness the heat in the ground around your home through the use of piping which contains water.

    As the water travels through the tubing, it is warmed by the latent heat in the ground.This heat is renewed on a daily basis by solar radiation.

    The heat then travels back into your home and is used to provide under floor heating to warm your home.This process is aided by the use of a heat exchanger.


    As with everything else there is a downside to this technology. If you install the heat collecting piping horizontally the area from which you collect the heat probably includes your food growing garden. Prolonged uses of geothermal heat collection during a hard cold winter will lower the surface ground temperature by a couple of degrees. This in turn may delay germination of seeds planted in this soil. Unless you are located in the far south this delay in getting your food plants going could affect the extent of your food crop.

    Drilling vertically for the ground heat usually involves several hundred feet and given the cost of drilling can become somewaht expensive. A friend opted for the vertical drilling approach because his property sits on a thick layer of gravel which does not retain as much heat as moisture filled soil. Unfortunately many locations in this area sits on bedrock where drilling costs become even more expensive.

    In suburban areas where many homes use geothermal a phenomena called ice lens can develop. An ice lens forms if too much heat is extracted from a closely spaced area so the underlying ground becomes deeply chilled and the frost in the ground is pulled much deeper than the normal.

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